The present invention relates to a new and improved process that integrates a nuclear closed-system regenerative gas turbine (Brayton) cycle, an open-system regenerative gas turbine cycle, and Rankine steam cycles.
Prior art advanced nuclear power plants employing regenerative Brayton cycles, such as the Modular Helium Reactor (˜600 thermal megawatts nuclear reactor) and the Pebble Bed Reactor (˜265 thermal megawatts nuclear reactor), are designed to provide a high level of safety by employing passive reactor emergency cooling systems. However, in order to achieve this level of safety, the thermal output of the reactor must be limited, which in turn restricts electrical energy production. The relatively high capital cost of the technology causes the installed cost of the power plant to be less competitive relative to more conventional technologies, such as combined cycle gas turbine cycles, in spite of the lower cost of the nuclear fuel.
The above advanced nuclear power plants are capable of achieving thermal efficiencies approaching 50 percent and electrical outputs of approaching 270 megawatts. This contrasts with advanced combined cycle power plant cycles, such as those using steam cooled gas turbines, that possess thermal efficiencies approaching 60 percent or more and net outputs beyond 700 megawatts. While the advanced nuclear plant efficiencies are impressive relative to the mid-30-percent efficiencies of conventional light water nuclear reactor power plants, the combined cycle power plants remain the choice of the market place, in spite of the low fuel costs and minimal air pollution associated with advanced and conventional nuclear power plants.
Prior art and planned advanced nuclear power plants employ regenerative Brayton cycles that utilize turbines directly coupled to electrical generators. In the event of the sudden loss of the generator's electrical load, rapid and severe pressure and thermal transients can occur in the reactor systems. Special design features are required in order to avoid damage to the reactor.
Prior art gas turbines and combined cycle power plants typically employ electrical generators directly coupled to the gas turbine and compressors that pressurize the working fluid. This arrangement causes the rotating equipment to operate at a constant speed. In order to reduce the electrical output of the generator, the firing temperature of the gas turbine must be reduced and/or air flow restricted by means dampers. Both of these methods adversely impact the thermal efficiency of the power plant, thereby increasing the cost to operate the facility as the electrical load is reduced. The power market is such that wide variations in power plant load requirements are a typical situation.
Prior art gas turbines have been proposed to utilize waste heat from the Brayton cycle to add vapor into the turbine working fluid at points downstream from the air compressors, with the added mass of the working fluid used to increase the output of the gas turbine while also decreasing compressor power needs. In effect, these cycles combine a Rankine steam cycle in parallel with the Brayton cycle by evaporating water into the working fluid. In general, Brayton cycles become more efficient at higher working fluid pressures, which lead to corresponding higher compressor discharge temperatures. However, the humidification process is practically more effective at lower pressures. Further, the waste heat utilized by the evaporation process is, by definition, associated with lower temperatures from which useful energy could not otherwise be extracted.
Prior art combined cycle power plants can increase steam production (and ultimately, electrical generation) by combusting fuel using duct burners located in a heat recovery steam generator unit. However, the increased generation is at the expense of a reduction in overall thermal cycle efficiency because a single working fluid (water) and thermal cycle (Rankine steam cycle) are used.
Prior art advanced combined cycle power plants, while very efficient, still require large quantities of fuel fired in the gas turbines that drive the generators used to produce electrical energy as well as drive the compressors that pressurize the working fluid. The fuel can represent more than 70 percent of the cost to operate the facility. Fuel prices can be volatile, which can cause difficulties in the financial structure of the power plant investment.
The power industry is faced with increasingly restrictive regulations concerning all types of emissions as a result of the collective desire for a cleaner environment. These restrictions are becoming progressively more difficult for fossil fuel facilities to achieve.
Prior art coal gasification plants are able to achieve relatively clean air emissions when the fuel produced by the gasifier is fired in combustion turbines. However, the capital cost of the integrated gasification combined cycle (IGCC) plant is high, thus causing the cost of energy produced from the facilities to be marginally competitive, at best. In addition, the units can produce hydrogen for possible use as an energy source, but at high costs and with limited production capabilities.
Accordingly, there is a need to develop a more integrated solution to the above issues.